Systems, methods, and devices for radiation beam asymmetry measurements using electronic portal imaging devices

ABSTRACT

Systems and methods for determining beam asymmetry in a radiation treatment system using electronic portal imaging devices (EPIDs) without implementation of elaborate and complex EPID calibration procedures. The beam asymmetry is determined based on radiation scattered from different points in the radiation beam and measured with the same region of interest ROI of the EPID.

FIELD

The present disclosure relates generally to radiation therapy, and morespecifically to systems and methods for using electronic portal imagingdevices (EPIDs) as radiation beam asymmetry measuring devices withoutthe need for implementing elaborate EPID calibration processes.

BACKGROUND

In radiosurgery or radiotherapy (collectively referred to as radiationtherapy) very intense and precisely collimated doses of radiation aredelivered to a target region (volume of tumorous tissue) in the body ofa patient in order to treat or destroy tumors or other lesions such asblood clots, cysts, aneurysms or inflammatory masses, for example.Patients undergoing radiation therapy are typically placed on thetreatment platform of a radiation treatment gantry. The radiation beamirradiates a region of interest in the patient, such as a diseasedtissue including a tumor or cancerous growth site. When delivering theradiation, a plurality of radiation beams may be directed to the targetarea of interest from several positions outside the body.

The goal of radiation therapy is to accurately deliver a prescribedradiation dose to the tumor/lesion and spare the surrounding healthytissue. The geometric accuracy of patient positioning relative to thetreatment beam, as well as the location and amount of dose delivered tothe patient is therefore important. There are a number of factors thatcould affect geometric and dose delivery accuracy, including but notlimited to, radiation beam symmetry. A radiation beam which is notsymmetric may introduce errors in the radiation beam delivered onto thepatient.

Beam symmetry depends on the accurate alignment and placement of variousmechanical elements/pieces of the radiation therapy system. Therefore,the mechanical elements need to be checked and tuned prior to theradiation treatment device being installed and/or used in the radiationtreatment facility. Because the mechanical elements affecting beamsymmetry tend to move, the beam symmetry needs also to be regularlychecked and, if a shift or movement is observed from the mechanicalelements' nominal preset values, the mechanical elements need to beadjusted and retuned during installment, and verified during regularpreventive maintenance inspection. Also, the radiation dose amount anddose placement need to be sufficiently controlled for accurate patienttreatment. Therefore, the radiation therapy machine itself needs to beproperly tuned at the outset (on the production floor), and thencontinuously monitored through periodic checks, such as, during initialinstallation or during routine usage of the machine by the customer, toensure that the system is operating within appropriate and expectedparameters and standards, such as, but not limited to, standardsprescribed by a nationally recognized regulatory groups, such as, theAmerican College of Radiology (ACR), the American Association ofPhysicists in Medicine (AAPM), or the Society for Imaging Informatics inMedicine (SIIM), for example.

Electronic portal imaging devices (EPIDs) have been previously used forevaluating beam symmetry and for verification of treatment beams.Generally, these EPIDs are used as relative dose or absolute dosemeasuring devices, whereby images obtained using an EPID are comparedwith previously obtained images, and the discrepancies between theimages are associated with the parameters of the system. However, inorder to make such a comparison, the images must be corrected fornon-linear behavior of the electronics, inhomogeneous pixelsensitivities, scattering in the detector, and the EPID panel's complexenergy response. These correction methods are complex. For example,EPIDs used as relative dose measurement devices require an externalreference measurement of some sort, and the corresponding calibrationschemes are often tedious. EPIDs used as absolute dose measuring deviceson the other hand require complex and time-consuming calibrationtechniques to correct for non-linearity of the EPID response. Thesecalibration techniques also require accurate motion control of the EPID.

There is thus a need for methods, systems, and devices by which EPIDscan be used as measurement devices for beam symmetry and beam alignmentwithout having to implement elaborate calibration procedures. Since manyof the modern radiation treatment devices, such as medical LINACS, areequipped with electronic portal imaging devices (EPIDs), there is a needfor a process that enables using the EPIDs as beam alignment measuringdevices without extensive calibration protocols in place, in order toperform automatic calibration, tuning, and verification of the radiationtreatment systems and devices. Since currently available radiationtherapy machine tuning, calibration, and verification protocols areslow, inaccurate, require external hardware, and/or rely on subjectivehuman decisions, this would reduce overall costs, processing, andanalysis time, as well as remove operator dependency.

SUMMARY

An object of the present disclosure is to provide a system and methodfor using an electronic portal imaging device (EPID) as a radiation beamsymmetry determining device and beam alignment device without the needfor extensive EPID calibration.

In exemplary embodiments, beam symmetry is determined by generatingscattered radiation at a plurality of points in a radiation beam,measuring the radiation scattered from the plurality of points using thesame region of interest ROI of the imaging device, and determining abeam asymmetry value based on the measured scattered radiation.

In an embodiment, the ROI is a circular ROI that has a center located atthe same position as the projection of the collimator rotation axis onthe imaging plane of the imaging device. In other embodiments, the ROIis not circularly symmetric around the projection of the collimatorrotation axis on the imaging device. In another exemplary embodiment,the radiation delivery system includes a collimator, and the generatingof the scattered radiation at the plurality of points in the radiationbeam includes generating an off-axis field using the collimator,rotating the collimator around a collimator rotation axis from a firstcollimator location to a plurality of different subsequent collimatorlocations, and illuminating the collimator with the radiation beam atthe first and subsequent collimator locations. The beam asymmetry valuecan be calculated using:

A_(ij)=(p_(i)−p_(j))/(p_(i)+p_(j)), where A_(ij) is the asymmetry value,p_(i) is an amplitude of the scattered radiation measured at the firstcollimator location, and p_(j) is an amplitude of the scatteredradiation measured at a second subsequent collimator location.

In another exemplary embodiment, the radiation beam tilt relative to thecollimator axis of rotation can also be determined using the calculatedasymmetry value. The radiation beam can be further aligned automaticallyand/or manually based on the determined radiation beam tilt.

In other exemplary embodiments, a method of determining radiation beamasymmetry is disclosed, comprising: moving a scatter probe from a firstlocation to a second, symmetric location in a radiation field,irradiating the scatter probe at the first and second locations withradiation, measuring radiation scattered by the scatter probe at thefirst location and radiation scattered by the scatter probe at thesecond location using an imaging device, and calculating a beamasymmetry value based on the measured scattered radiations. Thescattered radiation can be created by a small off-axis field which canbe generated using a collimator, and the moving of the scatter probe canbe done by moving the collimator around a collimator rotation axis froma first to a second collimator location.

In embodiments, the measuring of the scattered radiation at the firstlocation includes detecting in a detection plane of the imaging device aplurality of first intensity values from pixels located in a region ofinterest ROI of the imaging device and determining a first amplitude ofthe scattered radiation (p_(i)) based on the plurality of firstintensity values, and the measuring of the scattered radiation at thesecond location includes detecting a plurality of second intensityvalues from the pixels located in the same region of interest ROI of theimaging device and determining a second amplitude of the scatteredradiation (p_(j)) based on the second pixel intensity values. Inembodiments, the region of interest ROI is a region that is circularlysymmetric around a projection of the collimator rotation axis on theplane of the imaging device.

In embodiments, a radiation treatment system for implementing disclosedbeam symmetry determination methods based on scattering radiationmeasurements from different scattering locations in the radiation beamis also disclosed, the system exemplarily comprising: a radiation sourceto emit a radiation beam, a collimator configured to shape the radiationbeam, an imaging device configured to detect the radiation beam, and aprocessing device configured to execute processor-executable processsteps for determining radiation beam characteristics withoutimplementing an imaging device response calibration protocol, theprocess steps comprising:

generating scattered radiation from a plurality of points in theradiation beam;

measuring the scattered radiation from the plurality of points using theimaging device;

determining one or more characteristics of the radiation beam from themeasured scattered radiation; and

calibrating the radiation treatment system based on the determined oneor more radiation beam characteristics.

In embodiments, the measuring of the scattered radiation includesmeasuring the scattered radiation using pixels of the imaging devicepositioned in the same region of interest ROI of the imaging device foreach of the plurality of points in the radiation beam. The region ofinterest ROI can be a region that is circularly symmetric around aprojection of the collimator rotation axis on the plane of the imagingdevice.

The present disclosure also provides using an EPID as a measuring devicefor detecting beam asymmetry in a radiation treatment device,calculating an asymmetry value from the detected asymmetry, and usingthe asymmetry value to modify the performance of the radiation therapysystem to achieve the desired tuning and calibration of the system.

Another object of the present invention is to provide methods forautomatic calibration, tuning, and verification of radiation treatmentdevices and systems to eliminate beam asymmetry using an uncalibratedEPID.

Another object of the present invention is to provide specificprocedures and algorithms for the automatic tuning, calibration, andverification protocols using an EPID as a beam asymmetry measuring andbeam alignment device without having to implement complex calibrationprocedures.

The present disclosure also provides radiation treatment systems,comprising: a radiation source configured to emit a radiation beam, animaging device configured to acquire one or more images, and aprocessing device configured to execute processor-executable processsteps for determining radiation beam characteristics withoutimplementing an imaging device response calibration protocol.

The present disclosure also provides for systems and methods forcalibrating the radiation treatment system based on the determined oneor more radiation beam characteristics. The calibrating can includecalibrating control elements of the radiation treatment system, thecontrol elements controlling the characteristics of the radiation beam.The control elements can include one or more of beam collimator devices,beam angle steering coils, beam position steering coils, shunt currentsources, beam flattening filters, beam scattering filters, dosimeters,gantry positioning devices, light sources, beam sources, and gun-cathodeheating controls.

The present disclosure also provides systems, devices, and methods forfast and less error prone tuning, calibration, and verification ofradiation therapy systems based on scattering measurements obtainedusing electronic portal imaging devices, without the implementation ofan EPID response calibration procedure.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will hereinafter be described with reference to theaccompanying drawings, which have not necessarily been drawn to scale.Where applicable, some features may not be illustrated to assist in theillustration and description of underlying features.

FIG. 1 illustrates a radiation treatment system according to one or moreembodiments of the disclosed subject matter.

FIGS. 2A and 2B illustrate the rotation axes and coordinate frameorientation of the radiation treatment device of FIG. 1.

FIG. 3 illustrates a linac treatment head used in a radiation treatmentsystem operating in a photon generation mode.

FIG. 4 illustrates a linac treatment head used in a radiation treatmentsystem operating in an electron-beam generation mode.

FIGS. 5A-5B illustrate an exemplary imaging device used in the radiationtreatment device of FIG. 1.

FIG. 6 illustrates a correlation between the beam center, collimatorrotation axis, collimator rotation center, and a radiation source for anexemplary embodiment using an EPID.

FIG. 7 illustrates field edges and comb patterns formed by a collimatorused in the radiation treatment device of FIG. 1.

FIG. 8 illustrates an example of how the detected edges at differentcollimator angles are combined according to an exemplary embodiment.

FIG. 9 illustrates an example of a symmetric beam.

FIG. 10 illustrates an asymmetric beam obtained from a tilt of theradiation source.

FIG. 11 illustrates different positions of a scattering probe in theradiation field.

FIG. 12 illustrates a region of interest ROI around a beam center for aradiation field according to an exemplary embodiment.

FIG. 13 illustrates an exemplary radiation beam profile generated by aradiation beam.

FIGS. 14, 14A and 14B illustrate two-dimensional angular scatteredradiation intensity distributions around the radiation beam centeraccording to different exemplary embodiments.

FIG. 15A illustrates positions of the collimator jaws for a symmetricradiation field, according to an exemplary embodiment.

FIG. 15B illustrates positions of the collimator jaws for generating asmall off-axis field according to an exemplary embodiment.

FIG. 16 illustrates positions of the collimator jaws and MLC forgenerating a small off-axis field according to an exemplary embodiment.

FIG. 17 illustrates an exemplary flow diagram for adjusting radiationtilt based on determined beam asymmetry using an EPID according to anembodiment.

FIG. 18 illustrates an exemplary flow diagram for determining beamsymmetry based on measured scattered radiation using an EPID accordingto an embodiment.

FIG. 19 illustrates an exemplary flow diagram for a calibration processusing an EPID according to one or more embodiments of the disclosedsubject matter.

FIG. 20 illustrates an example for graphical indicators for bolt turnsto correct misalignment according to an exemplary embodiment.

DETAILED DESCRIPTION

An exemplary radiation therapy treatment system which uses an EPID as abeam symmetry measuring device is illustrated in FIG. 1. The treatmentsystem 100 is configured to deliver radiation treatment to a patient101. The treatment system 100 can be configured for dual-modestereotactic or radiation therapy application, namely, the system 100can be configured to provide photon-based or electron-beam basedradiation treatment to a patient 101 positioned on a treatment couch102. The gantry 106 can be a ring gantry (i.e., it extends through afull 360° arc to create a complete ring or circle), but other types ofmounting arrangements may also be employed. For example, a static beam,or a C-type, partial ring gantry, or robotic arm can be used. Any otherframework capable of positioning the treatment beam source at variousrotational and/or axial positions relative to the patient 101 may alsobe used. The system 100 also includes a treatment couch 102 which can bepositioned adjacent to the gantry 106 to place the patient 101 and thetarget volume within the range of operation of the treatment beam duringradiation treatment. The treatment couch 102 may be connected to therotatable gantry 106 via a communications network and is capable oftranslating in multiple planes to reposition the patient 101 and thetarget volume. The treatment couch 102 can have three or more degrees offreedom.

The radiation therapy system 100 includes a radiation treatment device103, such as, but not limited to, a dual-mode (photon and electron-beam)medical LINAC device configured for stereotactic or radiation therapyapplication. The radiotherapy device 103 includes a base or supportstructure 104 supporting the gantry 106. The gantry 106 is supporting anelectron beam accelerator module 108 which can include an electron gun114 for generating electron beams and an accelerator waveguide 115 foraccelerating the electron beams from the electron gun 114 toward anX-ray target 118 (when the radiation treatment device 103 operates in aphoton mode) or toward an electron beam exit window (not shown), whenthe radiation treatment device 103 operates in an electron-beam mode.The electron beam exit window allows the electron beam to exit theelectron beam accelerator module 108 and enter a LINAC treatment head110. The accelerating waveguide 115 can be mounted parallel to thegantry rotation axis, and thus the accelerated electron beam must bebent for it to strike the X-ray target 118 (when device 103 operates inthe photon mode) or the exit window (when device 103 operates in anelectron-beam mode). The accelerating waveguide 115 can also be mountedparallel to the collimator rotation axis. An electron beam transportsystem 116 can include bending magnets, steering coils, trim coils, anda gun cathode heating circuit can be used for bending and steering theaccelerated electron beams toward the X-ray target 118 or the exitwindow. In alternative embodiments, the electron beam transport system116 does not include bending magnets. The electron beam transport system116 can bend an electron beam at 90 degrees, 270 degrees (achromaticbending) and at 112.5 degrees (slalom bending) by adjusting the shuntcurrent applied to the bend magnet from a current source (not shown).When the electron pencil beam hits the X-ray target 118, it generatesthe clinical photon beams (X-rays, i.e., treatment beam). The locationat which the X-rays are generated is referred to as the radiation beamspot or radiation source.

In operation, electrons originating in the electron gun 114 areaccelerated in the accelerating waveguide 115 to the desired kineticenergy and then brought, in the form of a pencil electron beam, throughthe beam accelerator module 108 into the LINAC treatment head 110, wherethe clinical photons, such as X-rays, (when the device 103 operates inthe photon mode) or the electron beams (when device 103 operates in theelectron-beam mode) are produced. The LINAC treatment head 110 containsseveral components that influence the production, shaping, localizing,and monitoring of the clinical photon beams, as shown in detail in FIG.3, or the clinical electron beams, as shown in detail in FIG. 4.

The radiation treatment device 103 also includes a holding structure113, which could be a retractable robotic, servo controlled arm, holdingan imager 112 for acquiring digital images. The imager 112 is anelectronic portal imaging device (EPID). The holding structure 113 isused to position the EPID 112 and allows for the movement of the EPID112 vertically (along the Z-axis), laterally (along the X-axis), andlongitudinally (along the Y-axis). The EPID 112 can be mounted onto therotating gantry 106 in opposition to the radiation source, such that theclinical radiation beam, namely the photon or the electron beam, fromthe LINAC head 110 is received by the EPID 112. The EPID 112 can have adetector surface corresponding to the cross-sectional area of theclinical radiation beam.

In operation, the EPID 112 produces electronic signals providingmeasurements of the radiation received at the detector surface atregularly spaced positions over the detector surface. The signals fromthe EPID 112 are transmitted to a computer processor of the controller120 where it is converted into a matrix of digital values, the valuesindicating the dose of radiation at each point of the imager surface. Aprojection image derived from the matrix of digital values can bedisplayed on a display of the controller 120.

The controller 120 manages images and related information, such astransforming the data stream from the EPID 112 into a standard videoformat, the synchronization of the imager 112 and the LINAC treatmenthead 110 based on the different types of measurements acquired with theEPID 112, as well as data transfer, frame processing, and calibration.The controller 120 can also store and display the final image data, thedose image, as well as provide instructions for taking correctiveactions. Controller 120 can include a computer with typical hardware,such as a processor, and an operating system for running varioussoftware programs and/or communication applications. The computer caninclude software programs that operate to communicate with the radiationtreatment device 103, which software programs are operable to receivedata from external software programs and hardware. The computer can alsoinclude any suitable input/output devices adapted to be accessed bymedical personnel, as well as input/output (I/O) interfaces, storagedevices, memory, keyboard, mouse, monitor, printers, scanner, etc. Thecomputer can also be networked with other computers and radiationtherapy systems. Both the radiation therapy device 103 and thecontroller 120 can communicate with a network as well as a database andservers. The controller 120 can also be configured to transfer medicalimage related data between different pieces of medical equipment.

The system 100 also includes a plurality of modules containingprogrammed instructions (e.g., as part of controller 120, or as separatemodules within system 100, or integrated into other components of system100), which instructions cause system 100 to perform different tuning,calibration, and verification functions related to the radiationtreatment device 103, as discussed herein, when executed. The modulescan be written in C or C++ programming languages, for example. Computerprogram code for carrying out operations as described herein may also bewritten in other programming languages.

The system 100 including the EPID 112 integrated with the radiationtreatment device 103 allows for all radiation detection and radiationdata measurement related activities, as well as image guidanceactivities, such as, but not limited to, generation of scatteredradiation from different points in the radiation field, generation ofoff axis-fields, scattering data acquisition, scattering datainterpretation, EPID dark-field calibration, beam symmetrydetermination, asymmetry value calculation, image registration, imageinterpretation, EPID pixel calibration, and machine calibration to occurautomatically and remotely. System 100 also allows for scatteredradiation data acquisition, beam symmetry evaluation, beam asymmetryvalue calculation, and system calibration (i.e., data relating togantry, collimator jaws, MLC, radiation source, EPID, X-ray target, beamsteering coils, etc.). The data related to measured scattered radiationwhich is used to determine and evaluate different beam symmetry relatedparameters and characteristics of the radiation treatment device 103 canbe performed using different algorithms. The determination ofadjustments needed to be made in the control element outputs based onthe evaluated parameters and characteristics may also be determinedusing different algorithms. Once the required beam characteristics aredetermined, the necessary tuning and/or calibration and/or verificationprotocols are automatically sent to the radiation treatment device 103and the control elements are automatically or manually adjusted untiltheir outputs fall within accepted ranges. The adjusting can also bedone as a combination of automatic and manual adjustments. FIGS. 2A and2B illustrate the radiation beam central axis, the gantry rotation axis,the collimator rotation axis, and the isocenter of system 100.

FIG. 3 illustrates a LINAC treatment head 110 when the device 103operates in a photon mode. The LINAC treatment head 110 can include oneor more retractable X-ray targets 118 where clinical photon beams, suchas X-rays, are produced, one or more flattening filters (FF) 117, whichcan be mounted on a rotating carousel or sliding drawer for ease ofmechanical positioning of the filters 117 into the X-ray or photon beam,dual transmission ionization chambers 119, a collimating device (i.e.,collimator) including primary collimators 111, adjustable secondarycollimators with two upper jaws 121 and two independent lower jaws 123,multileaf collimators (MLC) 125, and a field defining light source 130.

Primary collimators 111 define a maximum circular radiation field, whichis then further truncated with the adjustable secondary collimators(121, 123) to produce rectangular and square fields at the LINACisocenter. The primary collimator 111 defines the largest availablecircular field size and is a conical opening that can be machined into atungsten shielding block, for example, with the sides of the conicalopening projecting on to edges of the X-ray target 118 on one end of theblock, and on to the flattening filters 117 on the other end. Thethickness of the shielding block is usually designed to attenuate theaverage primary X-ray beam intensity to less than 0.1% of the initialvalue. Any other applicable material besides tungsten can also be used.

The secondary beam defining collimators include four blocks, two formingthe upper jaws 121 and two forming the lower jaws 123. They can providerectangular and square fields at the LINAC isocenter, with sides of theorder of few millimeters up to 40 cm. Alternatively, the jaws could beindependent asymmetric jaws to provide asymmetric fields, such as onehalf or three quarter blocked fields in which one or two beam edges arecoincident with the beam central axis. The optional multileafcollimators (MLC) 125 can be made of 120 movable leaves with 0.5 cmand/or 1.0 cm leaf width, for example. For each beam direction, anoptimized intensity profile is realized by sequential delivery ofvarious subfields with optimized shapes and weights. When using MLCs,from one subfield to the next, the leaves may move with the radiationbeam on (i.e., dynamic multi-leaf collimation (DMLC)) or with theradiation beam off (i.e., segmented multi-leaf collimation (SMLC)). Suchan MLC system can cover fields up to 40×40 cm², for example, and canrequire 120 individually computer controlled motors and controlcircuits. Miniature versions of the MLC can also be used. For example,miniature MLCs that project 1.5-6 mm leaf widths and up to 10×10 cm²fields at the LINAC isocenter, could also be used.

The ionization chamber 119 could be a dual transmission ionizationchamber used for monitoring the photon radiation beam output as well asthe radial and transverse beam flatness. The ionization chamber 119 actsas an internal dosimeter, and can be permanently imbedded into the LINACtreatment head 110 to continuously monitor the radiation beam output.The ionization chamber 119 could also be sealed to make its responseindependent of ambient temperature and pressure. The ionization chamber119 can include a primary and a secondary ionization chamber with theprimary chamber measuring monitor units (MUs). Typically, thesensitivity of the chamber electrometry circuitry is adjusted in such away that 1 MU corresponds to a dose of 1 cGy delivered in a water ofphantom at the depth of dose maximum on the central beam axis whenirradiated with a 10×10 cm² field at a source to surface distance (SSD)of 100 cm. Once the operator preset number of MUs has been reached, theprimary ionization chamber circuitry shuts the radiation treatmentdevice 103 down and terminates the dose delivery to the patient 101.Before a new irradiation is initiated, the MU display is reset to zero.

In addition to monitoring the primary dose in MUs, the ionizationchamber 119 can also monitor other operating parameters such as the beamenergy, flatness and symmetry. Measurements of all of these additionalparameters requires that the ionization chamber electrodes of theprimary and secondary chambers be divided into several sectors, with theresulting signals used in automatic feedback circuits to steer theelectron beam through the accelerating waveguide 115 and the beamtransport system 116 and onto the X-ray target 118 or scattering foils127, thereby ensuring consistent beam flatness and symmetry.

The LINAC treatment head 110 can also include a field defining lightsource 130 to provide a convenient visual method for correctlypositioning the patient 101 for treatment using reference marks. Thelight source 130 may be mounted inside the collimator and can bepositioned at the location of the X-ray target 118 by a rotatingcarousel or a sliding drawer assembly, or it may be positioned to oneside of the collimator axis of rotation with the light reflected by amirror. In clinical operations, the light field illuminates an area thatcoincides with the radiation treatment field on the patient's skin andthe alignment of the light field with the skin marks on the patient isused as the final confirmation that the patient 101 is correctlypositioned with respect to the radiation beam.

When the radiation treatment device 103 operates in an electron-beammode, the LINAC treatment head 110 does not need the X-ray target 118and the flattening filters 117. FIG. 4 illustrates a LINAC treatmenthead 110 when the radiation treatment device 103 operates in theelectron-beam mode. To activate an electron-beam mode, both the X-raytarget 118 and the flattening filters 117 used in the photon mode areremoved from the electron pencil beam path. The electron pencil beamexits the beam accelerator module 108 through a thin window (not shown)usually made of beryllium, which minimizes the pencil beam scatteringand bremsstrahlung production. To produce clinical electron beams fromthe electron pencil beams, thin scattering foils 127 of a high atomicnumber (copper or lead, for example) are positioned into the electronpencil beam at the level of the flattening filters 117 in the X-raymode. In addition to the primary 111 and secondary collimators 121, 123,the clinical electron beams also rely on electron beam applicators(cones) 129 for beam collimation. The rest of the collimation and beamshaping elements are the same as in the photon-beam mode.

FIGS. 5A-5B illustrate an exemplary EPID 112 used to generate EPIDimages and scattered radiation data. The EPID 112 could be an amorphoussilicon type detector panel including a 1 mm copper plate 201 to providebuild-up and absorb scattered radiation, and a scintillating phosphorscreen 202 made of terbium doped gadolinium oxysulphide to convert theincident radiation to optical photons. The scintillating screen 202 canhave a thickness of 0.34 mm, for example. The EPID 112 can also includea pixel matrix 203 created from an array of 1024×768 or 1280×1280 pixelsi, where each pixel i is made up of a photodiode to integrate theincoming light and a thin film transistor (TFT) to act as athree-terminal switch for readout. The EPID 112 can also includeelectronics to read out the charge from the transistor and translate itinto an image data.

The imager 112 can also be enclosed in a protective plastic cover 204with an air gap 205 between the protective cover 204 and the copperplate 201. Alternatively, layers of foam and paper 206 can be includedbetween the protective cover 204 and the copper plate 201. Theprotective cover can be about 3 cm above the effective point ofmeasurement. The buildup at the active matrix can be equivalent to 8 mmof water, which means that the dose maximum has not been reached foreither of the energies of the device 103. The EPID can be positioned atsource to EPID distances (SDD) from 95 cm to 180 cm. It can also have anactive imaging area of 40×30 cm² or 43×43 cm², for example. The maximumframe acquisition rate can be 15 frames/second, the permitted dose rangecan be between 4-25 MV, and the permitted dose rates can be between50-600 MU/min, for example. The disclosed EPID 112 is, however, onlyexemplary, and any other applicable EPIDs can be used as the measuringdevice 112.

EPID as Beam (A)Symmetry Determination Device

A requirement in radiation therapy is that the radiation dose variationover the targeted volume (i.e., tumor site, for example) is limited sothat all points in the targeted volume receive the prescribed radiationdose within a tolerance range. One of the factors that influencesradiation dose variation is radiation beam symmetry. Radiation beamsymmetry is defined as the maximum ratio of radiation doses at twosymmetric points relative to the radiation beam center as it isprojected from the radiation source past the radiation limiting devices(primary collimators 111, collimator jaws 121, 123, MLC 125, and/orcones 129) to the isoplane. When the radiation beam is symmetric, twosymmetric points relative to the radiation beam center are exposed tothe same radiation dose. The more symmetric the radiation beam, the lessdose variation is present in the targeted volume.

The radiation beam center (O) is defined as the collimation rotationcenter at a certain height SDD projected from the radiation source ontothe imaging plane, as shown in FIG. 6. The collimation rotation centercan be calculated many different ways, including, by taking a pluralityof images (five, for example) with the collimator MLC rotating, andcalculating the collimation rotation center from the set of (five)images obtained. Generally, the MLC jaws or leaves at a first heightform a comb pattern, and the MLC jaws or leaves at a second, differentheight are used to shape the left/right field edges as shown in FIG. 7.In order to determine the collimation rotation center, the detectededges at different collimator angles are combined as shown in FIG. 8,for example. For each pair of subsequent edges, the angle bisector lineis calculated. This results in four angle bisectors. Ideally, this setof lines intersects at the center of rotation. A least squares approachis then applied for finding the point in space with the least distanceto all bisection lines. This point in space is the beam center O. Thisbeam center determination method is only exemplary, and any other beamcenter determination method can be applied.

If the radiation source is at the collimation rotation center as shownin FIG. 6, the radiation beam axis coincides with the collimatorrotation axis, and the beam center O is independent of the height of thecollimation element used to determine the center. If not, the beamcenter O is determined based on the difference between the sourceposition and the collimation rotation axis. Beam symmetry is consideredalong both the X-axis and the Y-axis, with the Z axis being from theradiation source to the isoplane, and the Y axis increasing from thecenter toward the gantry stand structure, as shown in FIGS. 2A and 2B.

Depending on the radiation treatment system, there are many sourcescausing a radiation beam not to be symmetric (i.e., asymmetric radiationbeam). For example, if the electron pencil beam hits the target 118 (inradial and transverse planes) so that the radiation source positioncoincides with the collimation rotation center, the resultant radiationbeam is symmetric relative to the radiation beam center O, as shown inFIG. 9. However, if the electron pencil beam hits the target 118 asshown in FIG. 10, namely, the electron pencil beam is tilted relative tothe collimator rotation axis, the radiation source will generateasymmetries in the radiation beam.

As previously discussed, EPIDs have been previously used to determinebeam symmetries. Such measurements, however, required that the EPIDs becalibrated using complex calibration algorithms to offset the effectsthat energy fluence, beam field size, dose rate, and photon energy hason the EPID pixel values.

In the present disclosure, systems and methods are provided that allowEPIDs to be used to determine beam symmetries in a radiation treatmentsystem 100 (regardless of whether flattening filters FF 117 are used ornot) without having to calibrate the EPID utilizing elaboratecalibration protocols. This can be done by generating scatteredradiation at different locations in the radiation field using a scatterprobe SP, as shown in FIGS. 11 and 12, measuring the scattered radiationfrom the different scatter probe SP locations, and evaluating thescattered radiation obtained from scatter locations (scatter points)which are symmetrically opposed to each other with respect to thecollimator rotation axis (locations A, B, for example) using the sameregion of interest ROI of the EPID 112 by comparing the measuredscattered radiations.

If the beam is symmetric, the amount of scattered radiation measured bythe pixels in a predetermined ROI from scatter points which aresymmetrically opposed to each other relative to the collimator rotationaxis, should be the same.

If the beam is not symmetric, the amount of scattered radiation measuredby the pixels in the same ROI from the symmetrically opposing scatterpoints will be different. Since the comparing is between the same pixelsin the same ROI, the correlation between the measurements only dependson the constancy of the EPID sensitivity within the ROI and not theactual pixel sensitivity values. Thus, a calibration of the EPID 112 todetermine actual pixel sensitivities is not needed for determining beamsymmetry.

In order to generate scattered radiation at different locations in theradiation field in a radiation treatment system 100, a small off-axisfield is generated and moved in a radially symmetric fashion around thecollimator rotation axis by rotating the collimator around thecollimator rotation axis from a first location to a plurality ofsubsequent locations within its 360-degree rotational angle. Byirradiating the small off-axis field at different collimator locations,scattered radiation is obtained from different locations in theradiation field. By evaluating the scattered radiation generated fromsymmetrically opposite locations in the radiation field with respect tothe collimator rotation axis, the beam symmetry can be evaluated.

In order to obtain scattered radiation from symmetrically oppositelocations, in an exemplary embodiment shown in FIGS. 13, 14, 14A and14B, the collimator is rotated from a first collimator location to asecond collimator location, which is 180 degrees from the firstlocation, for example, whereby the scatter probe SP, and thus, thelocation of the small off-axis field, is moved from a first location toa symmetrically opposite location with respect to the collimatorrotation axis. By evaluating the scattered radiation measured in apredetermined region of interest ROI of the EPID 112 when the collimatoris in the first location against the scattered radiation measured usingthe same region of interest ROI of the EPID 112 when the collimator isin the second location, the beam symmetry can be evaluated.

In order to make scatter measurements independent of asymmetries due tothe geometric collimation imperfections and the amount of collimatorrotation, the predetermined ROI is a circular region of interestcentered around the projection of the collimator axis of rotation on theEPID 112 (i.e., around the beam center O), as shown in FIGS. 12-14, 14Aand 14B. FIGS. 14, 14A and 14B also show two-dimensional angularscattered radiation intensity distributions obtained around theradiation beam center O on the EPID 112 plane for such a setup.

By measuring the amount of scattered radiation when the collimator ispositioned at a first location using the pixels of the EPID 112 that arelocated in a circular region of interest ROI around the beam center O,and comparing it to the amount of scattered radiation measured by thesame pixels in the same ROI of the EPID 112 when the collimator ispositioned at a second location, which is 180 degrees from the firstlocation, for example, the radiation beam symmetry can be evaluated. Ifthe measured scattered radiation in the ROI at the first collimatorlocation is the same as the measured scattered radiation in the same ROIat the second collimator location, the radiation beam is symmetric, asshown in FIG. 9. If the scattered radiations are not the same, the beamis not symmetric.

The amount of beam asymmetry can be determined based on the differencebetween the measured scattered radiations for the two collimatorlocations. The asymmetry value can further be correlated to the tilt ofthe electron beam with respect to the collimator rotation axis.

There are numerous ways to generate a small off-axis field in theradiation treatment system 100. In an exemplary embodiment, in aradiation treatment system 100 with a 10 cm×10 cm radiation field forexample, a small (i.e., 1-2 cm, for example) off-axis field can begenerated by positioning the upper jaws 121 and the lower jaws 123 ofthe collimator in specific locations relative to each other and relativeto the collimator rotation center. For example, in their originalpositions, both the upper jaws 121 and the lower jaws 123 are positionedso as to be symmetric around the collimator rotation center and thusaround the collimator rotation axis as shown in FIG. 15A. By moving theupper jaws 121 of the collimator off-center (i.e., away from thecollimator rotation center) so as to be offset by a first and a seconddistance d₁, d₂, respectively, while the lower jaws 123 are positionedsymmetrically around the collimator rotation center, and thus around thecollimator rotation axis, a small square or rectangular radiation fieldis generated through the exposed collimator aperture, as shown in FIG.15B. For a 10 cm×10 cm radiation field, the off-center distances d₁, d₂could be for example, 1.5 cm and 3.5 cm, respectively. This willgenerate a 1 cm×1 cm off-axis field (i.e., d cm×d cm). However, theoff-center distances of the upper jaws 121 as well as the sizes of thegenerated off-axis fields are only exemplary and any other off-centerdistances can be used to generate different off-axis fields.

After the upper and lower collimator jaws 121, 123 are in place togenerate the small off-axis field, and without a patient, the collimatoris irradiated with the radiation beam, and the EPID 112 collects andrecords the plurality of radiation intensity values, one for each pixel,and supplies the corresponding signals to a processing circuit forfurther processing. The processing circuit could be included in the EPIDread-out electronics, the EPID image acquisition circuit, and/or couldbe part of the controller 120. Then, the collimator is rotated by 180degrees, for example, from its initial first position i to a secondposition j. The second position does not have to be 180 degrees from itsoriginal first position, and instead could be any other location withinits 360-degree angle rotation. When in its second position j, thecollimator is again irradiated with the radiation beam, and the EPID 112again collects and records the plurality of radiation intensity values,one for each pixel, and supplies the corresponding signals to theprocessing circuit for further processing.

The processing circuit is programmed to process the intensity valuescollected at each EPID pixel and calculate a corresponding scatteredradiation amplitude value (p) for each collimator location. Theprocessing circuit is also programmed to select particular pixels of theEPID for further processing. For example, the processing circuit isprogrammed to select the pixels of a particular region of interest ROIof the EPID 112 for the further processing.

In an exemplary embodiment, the processing circuit is programmed toselect the pixels of a predetermined region of interest ROI of the EPID112 that is circularly symmetric around the beam center (O) on theimaging plane of the EPID 112 for further processing. The circularlysymmetric ROI can have a radius r that is equivalent to 10 pixels of theEPID 112, for example, as shown in FIG. 14. However, this ROI size isexemplary only and any other ROI size can be used. The scatteredradiation amplitude value p_(i) for the first collimator location i isthen calculated by adding the intensity values collected for the pixelsof the EPID 112 that are located in the selected ROI. The scatteredradiation amplitude value p_(j) for the second collimator location j iscalculated by adding the intensity values collected for the pixels ofthe EPID 112 that are located in the same ROI as the one used forcalculating the scattered radiation amplitude value p_(j). If necessary,a normalization step can be added to take into account variations of thetotal beam output between the measurement at the first collimatorlocation i and the second collimator location j.

The processing circuit is further programmed to compare the scatteredradiation amplitudes p_(i) and p_(j) and determine, based on thiscomparison, whether the radiation beam is symmetric relative to the beamcenter O, and thus relative to the collimator rotation axis. If thescattered radiation amplitude p_(i) is the same as the scatteredradiation amplitude p_(j), the processing circuit concludes that thebeam is symmetric.

The processing circuit is further programmed to determine asymmetriesdefined by the measured radiation intensity values by analyzing thescattering amplitude values p_(i) and p_(j). By comparing the scatteredradiation p_(i) obtained at the first collimator position i to thescattered radiation p_(j) measured when the collimator is in the secondlocation j, an asymmetry value A_(ij), representing the radiation beamoffset from the collimator rotation axis is obtained from:A _(ij)=(p _(i) −p _(j))/(p _(i) +p _(j))The processing circuit is further programmed to correlate the measuredasymmetry value A_(ij) with the electron pencil beam tilt angle.

In alternative embodiments, the small off-axis fields can be generatedby positioning the MLCs 125 off-center by a first and a second distanced₁, d₂, respectively, while the upper jaws 121 are positionedsymmetrically around the collimator rotation axis as shown in FIG. 16.The particular ways described herein to generate small off-axis fieldsare not limiting, however, and any other available and applicablemethods are contemplated herein.

In alternative embodiments, the EPID 112 can be exposed to basic offset(i.e., dark field) calibration prior to being used to measure thescattered radiation.

In alternative embodiments, regions of interest ROI of the EPID 112 thatare not centered at the beam center O can be used to determine beamasymmetries. In such embodiments, however, the ROls used need to besymmetric to each other with respect to the collimator rotation axis.

An exemplary process S100 by which an EPID 112, which is only calibratedfor basic offsets, is used to determine radiation beam asymmetry in theradiation treatment system 100, can be implemented as shown in FIG. 17.In Step S101, the EPID 112 is moved to a known distance SDD from theradiation source so as to be aligned on the propagation direction (Zaxis) of the radiation beam, namely, the radiation beam axis. Thedistance SDD could be anywhere from 95 to 180 cm, for example. In StepS102, a small off-axis field is generated in the system 100. The smalloff-axis field can be generated by moving the collimator jaws 121, 123and/or the MLC 125 a specific distance from the collimator rotation axisso as to together generate a small off-axis field through the collimatoraperture. After the upper and lower collimator jaws are in place, thecollimator is irradiated with the radiation beam, or the collimator ismoved to a first location first and then irradiated with the radiationbeam (S103), and the EPID 112 measures the radiation impinging on itssurface in S104. The sum of the values captured by the pixels of theEPID 112 which are located in a specific region of interest ROI of theEPID 112, the ROI being circularly symmetric around the beam center O(the beam center O representing the projection of the collimator axis ofrotation on the imaging plane of the EPID 112) and having a specificradius r, are recorded as the scattered radiation p_(i) obtained at thefirst collimator location i in S104. The collimator is next rotated to asecond collimator location j (S105), and in step S106, the sum of thevalues captured by the pixels of the EPID 112 which are located in thesame region of interest ROI of the EPID 112 as used to record thescattered radiation p_(i) obtained at the first collimator location i,are recorded as the scattering radiation p_(j) obtained at the secondcollimator location j. The second collimator location is such that theoff-axis field is moved to a symmetrically opposing second location fromthe first location relative to the collimator rotation axis.

The two values p_(i) and p_(j) are then compared to each other. In stepS107, an asymmetry value A_(ij) is calculated usingA_(ij)=(p_(i)−p_(j))/(p_(i)+p_(j)). If p_(i) and p_(j) are the same, theasymmetry value A_(ij) is zero and a determination is made that theradiation beam is symmetric. If the asymmetry value A_(ij) is not zero,a determination is made that the beam is not symmetric. In such a case,the asymmetry value represents the amount by which the radiation beam isoffset from the collimator rotation axis. Optionally, in step S108, thetilt is determined based on the calculated asymmetry value, and in stepS109, the angle of incidence of the electron pencil beam onto the targetis adjusted based on the determined tilt.

In alternate embodiments, if the difference between p_(i) and p_(j) isnot zero, but falls within an acceptable value range (i.e., tolerancerange), it is determined that the beam is symmetric, and if thedifference between p_(i) and p_(j) does not fall within an acceptablevalue range, it is determined that the beam is not symmetric.

Adjusting the angle of incidence of the electron pencil beam onto theX-ray target 118 can be accomplished by adjusting the angle steeringcoils in the radial and transverse directions, or with mechanicaladjustments of the guide on low energy radiation treatment devices.Since the angle of incidence of the electron pencil beam onto the X-raytarget 118 is adjusted by adjusting the angle steering coils in theradial and transverse directions, the angle steering coils of theradiation treatment device 103 are calibrated in the radial andtransverse angles so that the electron pencil beam hits the X-ray target118 at a perpendicular angle, or the guide is mechanically adjusted. Ifit is determined that the beam is not properly aligned, a signal is sentto the controller 120 to automatically adjust the angle steering coilsin the radial and transverse directions.

In another exemplary process S300 shown in FIG. 18, beam symmetry isdetermined by first generating scattered radiation from a plurality oflocations in the radiation beam (S301), then measuring the scatteredradiation from the plurality of locations using pixels of the sameregion of interest (ROI) of an imaging device (S302), followed bydetermining beam symmetry from the measured scattered radiation bycomparing the scattered radiation obtained for at least two differentlocations in the plurality of locations (S303), the two locations beingsymmetric to each other relative to the radiation beam axis. If thescattered radiation is the same for two of the plurality of locationswhich are symmetric to each other relative to the radiation beam axis,or the difference between the measured scattered radiation falls withina previously determined acceptable range, the beam is determined to besymmetric. Otherwise, the beam is asymmetric and a beam asymmetry valueis calculated based on the measured scattered radiations for the twolocations. Optionally, a tilt of the radiation beam is determined basedon the calculated asymmetry value. The system 100 can also be calibratedbased on the determined tilt. The calibration can be automatic, manual,or a combination of the two.

System Calibration Using EPID

An exemplary automatic tuning/calibration process S200 by which thesystem 100 is tuned/calibrated with an EPID to operate within expectedparameters is shown in FIG. 19. The process S200 includes measuring,using an electronic portal imaging device (EPID), the scatteredradiation obtained at different collimator locations using the sameregion of interest ROI of the EPID (S202), the radiation having beenscattered by a scatter probe simulated by an off-axis field generated inthe radiation treatment system 100, and determining beam symmetry fromthe measured scattered radiation in S203. If it is determined in S203that the beam is not symmetric, a beam asymmetry value S205 iscalculated based on the measured scattered radiation in S203, followedby the step of tuning/calibrating the control elements of the system 100(S206) based on the calculated asymmetry value so as to ensure that themechanical and geometric integrity of the radiation treatment device 103is maintained. The process is repeated until it is determined in stepS203 that the beam is symmetric. At such time, the process ends at S204.Process S200 includes steps which use the EPID 112 to measure aradiation beam asymmetry value and use of the beam asymmetry value forthe mechanical element calibration/tuning/adjustment process by whichthe radiation beam is aligned.

The calibration process S200 includes a plurality of calibration taskswhich could be fully or partially automatically performed using anelectronic portal imaging device EPID 112. The starting of thetuning/calibration process S200 can be initiated at the controller 120in Step S201, or via a second computer adapted to communicate withcontroller 120 to execute the calibration tests. In one embodiment, theprocess S200 provides for an automated test sequence that quicklydetermines beam asymmetry and completes tests to help medical physicistsdetermine whether the radiation therapy system is operating withinspecified parameters prior to treatment.

Using the EPID 112 in the process S200 allows for the determination ofbeam symmetry change with respect to a reference (e.g., baseline). Thedetermined discrepancies between the measured beam symmetry values andthe baseline beam symmetry values can be displayed for service purposes,as shown in FIG. 20, so that the angle steering coil could be adjustedaccordingly.

The system calibration process S200 also includes determining beam tiltand initiating the appropriate calibration of the beam if adetermination is made that there is a beam tilt relative to thecollimator rotation axis. The process S200 provides the ability tomeasure radial and transversal source offset and tilt with gantry at anyposition. The calibration process S200 also provides the ability toreview completed measurements at any time, as well as visual indicatorsfor suggested alignment procedures including alignment bolts correctionturns, as shown in FIG. 20.

Embodiments described herein therefore provide systems and methods wherean EPID can be used as a measurement device for measuring differentparameters of the radiation treatment system, without having toimplement a complex calibration of the EPID. The general process bywhich the radiation treatment system and device 103 is automaticallycalibrated using an electronic portal imaging device (EPID) includes thesteps of evaluating various parameters of the radiation treatment device103, followed by the automatic tuning of various elements of theradiation treatment device in response to the result of the evaluation.This can be achieved by measuring scattered radiation from differentlocations of a scatter probe (off-axis field) in a radiation field usingthe same predetermined region of interest ROI of the EPID 112 anddetermining a parameter of the radiation treatment device 103. Thisparameter can be any one of beam symmetry, tilt, and beam alignment.

Then each parameter is evaluated to determine whether it falls within aprescribed range. If the parameter falls within a prescribed range, theprocess steps are repeated to determine and evaluate another parameterof the radiation treatment device 103. If the parameter does not fallwithin a prescribed range, the output of a control element of theradiation treatment device 103 affecting the respective parameter isadjusted until the parameter falls within the prescribed range. Theadjustment can include an adjustment in the radiation limiting(collimating) devices, the angle and position of the steering coils, thelocation of the flattening filters 117, the size of the bend magnetshunt current, and the position and symmetry of the ionization chamber119, for example. The adjustment can also be done manually, whereappropriate. For example, manual adjustment of mechanical screws, bolts,or any other mechanical pieces of the radiation treatment system can bemanually done.

This calibration process can be automatically repeated until some or allparameters of the device are evaluated and the corresponding controlelement outputs adjusted. Any number of automatic routines using anydifferent type of feedback device can be inserted in the calibrationprocess with the same iterative tuning. When all the outputs are tunedand the evaluated parameters fall within prescribed ranges, theradiation treatment device 103 is properly tuned, and the process stops.

It will be appreciated that the processes, systems, and sectionsdescribed above can be implemented in hardware, hardware programmed bysoftware, software instruction stored on a non-transitory computerreadable medium or a combination of the above. For example, a method canbe implemented using a processor configured to execute a sequence ofprogrammed instructions stored on a non-transitory computer readablemedium. The processor can include, but not be limited to, a personalcomputer or workstation or other such computing system that includes aprocessor, microprocessor, microcontroller device, or is comprised ofcontrol logic including integrated circuits such as, for example, anApplication Specific Integrated Circuit (ASIC). The instructions can becompiled from source code instructions provided in accordance with aprogramming language such as Java, C++, C # or the like. Theinstructions can also comprise code and data objects provided inaccordance with, for example, the Visual Basic™ language, LabVIEW, oranother structured or object-oriented programming language. The sequenceof programmed instructions and data associated therewith can be storedin a non-transitory computer-readable medium such as a computer memoryor storage device which may be any suitable memory apparatus, such as,but not limited to read-only memory (ROM), programmable read-only memory(PROM), electrically erasable programmable read-only memory (EEPROM),random-access memory (RAM), flash memory, disk drive and the like.

Furthermore, the modules, processes, systems, and sections can beimplemented as a single processor or as a distributed processor.Further, it should be appreciated that the steps mentioned above may beperformed on a single or distributed processor (single and/ormulti-core). Also, the processes, modules, and sub-modules described inthe various figures of and for embodiments above may be distributedacross multiple computers or systems or may be co-located in a singleprocessor or system.

The modules, processors or systems described above can be implemented asa programmed general purpose computer, an electronic device programmedwith microcode, a hard-wired analog logic circuit, software stored on acomputer-readable medium or signal, an optical computing device, anetworked system of electronic and/or optical devices, a special purposecomputing device, an integrated circuit device, a semiconductor chip,and a software module or object stored on a computer-readable medium orsignal, for example.

Embodiments of the method and system (or their sub-components ormodules), may be implemented on a general-purpose computer, aspecial-purpose computer, a programmed microprocessor or microcontrollerand peripheral integrated circuit element, an ASIC or other integratedcircuit, a digital signal processor, a hardwired electronic or logiccircuit such as a discrete element circuit, a programmed logic circuitsuch as a programmable logic device (PLD), programmable logic array(PLA), field-programmable gate array (FPGA), programmable array logic(PAL) device, or the like. In general, any process capable ofimplementing the functions or steps described herein can be used toimplement embodiments of the method, system, or a computer programproduct (software program stored on a non-transitory computer readablemedium).

Furthermore, embodiments of the disclosed method, system, and computerprogram product may be readily implemented, fully or partially, insoftware using, for example, object or object-oriented softwaredevelopment environments that provide portable source code that can beused on a variety of computer platforms.

Alternatively, embodiments of the disclosed method, system, and computerprogram product can be implemented partially or fully in hardware using,for example, standard logic circuits or a very-large-scale integration(VLSI) design. Other hardware or software can be used to implementembodiments depending on the speed and/or efficiency requirements of thesystems, the particular function, and/or particular software or hardwaresystem, microprocessor, or microcomputer being utilized.

Features of the disclosed embodiments may be combined, rearranged,omitted, etc., within the scope of the invention to produce additionalembodiments. Furthermore, certain features may sometimes be used toadvantage without a corresponding use of other features.

It is thus apparent that there is provided in accordance with thepresent disclosure, systems, methods, devices, and algorithms for usingan EPID as a measuring device for beam tilt and beam asymmetrydetermination without having to calibrate the EPID. It is thus alsoapparent that there is provided in accordance with the presentdisclosure, systems, methods, devices, and algorithms for using an EPIDas an imaging device for calibrating a radiation treatment systemwithout needing to implement extensive and complex calibrationprocedures.

Many alternatives, modifications, and variations are enabled by thepresent disclosure. While specific embodiments have been shown anddescribed in detail to illustrate the application of the principles ofthe present invention, it will be understood that the invention may beembodied otherwise without departing from such principles. Accordingly,Applicants intend to embrace all such alternatives, modifications,equivalents, and variations that are within the spirit and scope of thepresent invention.

What is claimed is:
 1. A system for determining radiation beam symmetryin a radiation device, comprising: an imaging device configured tomeasure radiation scattered from a first scatter aperture and a secondscatter aperture generated in a radiation field of the radiation device,the first and second scatter apertures being symmetric to each other;and a processor configured to calculate a beam asymmetry value based onthe measured scattered radiation, wherein the beam asymmetry value iscalculated based on an amplitude of the scattered radiation from thefirst scatter aperture and an amplitude of the scattered radiation fromthe second scatter aperture.
 2. The system of claim 1, wherein the firstand second scatter apertures are generated using a collimator of theradiation device, the collimator being configured to rotate around acollimator rotation axis.
 3. The system of claim 2, wherein the firstand second scatter apertures are generated by creating an off-axis fieldusing the collimator and rotating the collimator around the collimatorrotation axis from a first collimator location to a second collimatorlocation, the second collimator location being rotationally symmetric tothe first collimator location.
 4. The system of claim 3, wherein theoff-axis field is generated by positioning at least an element of thecollimator so as to be offset relative to the collimator rotation axis.5. The system of claim 4, wherein the generated off-axis field is a 1-2cm rectangular or square radiation field.
 6. The system of claim 3,wherein the imaging device is an electronic portal dose imaging device(EPID), and the scattered radiation is measured using a plurality ofpixels located in a region of interest ROI of the EPID.
 7. The system ofclaim 6, wherein the region of interest ROI is circularly symmetricaround a projection of the collimator rotation axis on the plane of theEPID.
 8. The system of claim 1, wherein the processor is furtherconfigured to determine radiation beam tilt relative to the collimatorrotation axis using the calculated asymmetry value, and furtherconfigured to initiate alignment of the radiation beam in the radiationdevice based on the determined radiation beam tilt.
 9. A radiationtreatment system, comprising: a radiation source configured to emit aradiation beam onto a collimator; the collimator being configured torotate around a collimator rotation axis so as to generate a firstscatter aperture in the radiation beam at a first location of thecollimator, and a second scatter aperture at a second, symmetriclocation of the collimator; an imaging device configured to measureradiation scattered from the first and second scatter apertures; and aprocessing device configured to calculate a radiation beam asymmetryvalue based on the measured scattered radiation, wherein the measuringof the scattered radiation includes measuring the scattered radiationusing pixels of the imaging device positioned in the same region ofinterest ROI of the imaging device for each of the first and secondscatter apertures.
 10. The system of claim 9, wherein the first andsecond scatter apertures are generated by creating an off-axis fieldusing the collimator and rotating the collimator around the collimatorrotation axis from a first collimator location to a second collimatorlocation, the second collimator location being rotationally symmetric tothe first collimator location.
 11. The system of claim 10, wherein theoff-axis field is generated by positioning at least an element of thecollimator so as to be offset relative to the collimator rotation axis,and wherein the generated off-axis field is a 1-2 cm rectangular orsquare radiation field.
 12. The system of claim 10, wherein the imagingdevice is an electronic portal dose imaging device (EPID), and thescattered radiation is measured using a plurality of pixels located inthe region of interest ROI of the EPID.
 13. The system of claim 12,wherein the region of interest ROI is circularly symmetric around aprojection of the collimator rotation axis on the plane of the EPID. 14.The system of claim 9, wherein the processor is further configured todetermine radiation beam tilt relative to the collimator rotation axisusing the calculated asymmetry value, and further configured to initiatealignment of the radiation beam in the system based on the determinedradiation beam tilt.
 15. A non-transitory computer-readable storagemedium upon which is embodied a sequence of programmed instructions fordetermining radiation beam symmetry in a radiation therapy system, and acomputer processing device which executes the sequence of programmedinstructions to cause the computer processing device to: generate afirst and a second, symmetric scatter aperture in the radiation field;illuminate the first and the second scatter apertures with radiation;measure the radiation scattered from the first scatter aperture and thescattered radiation from the second scatter aperture; and calculate anasymmetry value from the measured first and second scattered radiation.16. The non-transitory computer-readable storage medium of claim 15,wherein the first and second scatter apertures are generated using acollimator of the radiation therapy system, the collimator beingconfigured to rotate around a collimator rotation axis.
 17. Thenon-transitory computer-readable storage medium of claim 16, wherein thefirst and second scatter apertures are generated by creating an off-axisfield using the collimator and rotating the collimator around thecollimator rotation axis from a first collimator location to a secondcollimator location, the second collimator location being rotationallysymmetric to the first collimator location.
 18. The non-transitorycomputer-readable storage medium of claim 17, wherein the off-axis fieldis generated by positioning at least an element of the collimator so asto be offset relative to the collimator rotation axis, the generatedoff-axis field being a 1-2 cm rectangular or square radiation field. 19.The non-transitory computer-readable storage medium of claim 18, whereinthe scattered radiation is measured using a plurality of pixels locatedin a region of interest ROI of an imaging device, the region of interestROI being circularly symmetric around a projection of the collimatorrotation axis on the plane of the imaging device.
 20. The non-transitorycomputer-readable storage medium of claim 19, wherein the computerprocessing device determines radiation beam tilt relative to thecollimator rotation axis using the calculated asymmetry value, andaligns the radiation beam based on the determined radiation beam tilt.